This invention relates to an image formation apparatus with a cartridge for housing a roll of photosensitive sheet.
Of particular interest for application of this invention are photosensitive sheets of the type disclosed, for example, in Japanese Patent Publication Tokkai No. 58-88739 comprised of a flexible base sheet coated with microcapsules encapsulating a colorless dye and a photopolymerizing agent which hardens by exposure to light. When a photosensitive sheet like this is exposed to an image forming beam of light such as reflected light from an original document to be copied, those of the microcapsules exposed to light harden while those not exposed remain soft such that an invisible image, or a pattern, of selectively hardened microcapsules is formed on the sheet. A visible image can be obtained from such an invisible image by superposingly covering the invisible pattern with an image transfer sheet coated with a developer material and pressing them together such that only those of the microcapsules which are not hardened by exposure to light are ruptured, causing the encapsulated colorless dye to flow out. The developer material is so selected as to have a chromogenic effect on the dye encapsulated in the microcapsules. Thus, the dye flowing out of the ruptured microcapsules becomes visible, producing a visible image on the transfer sheet.
In an image formation process of this type, it is important to protect the surface of the photosensitive sheet coated with microcapsules not only against external light but also against external force before it is exposed to the image forming beam of light because an external force may rupture the microcapsules. One method of achieving this is to prepare the photosensitive sheet in the form of a roll and set it inside the housing structure of the image formation apparatus. An additional advantage of preparing the photosensitive sheet in a rolled form is that it can then be directly wound around a cylindrical drum on the surface of which an exposure point is defined by an optical system. In this manner, the photosensitive sheet can be supplied and transported by the rotation of this drum and feeding rollers and the like for transporting cut sheets from a cassette can be dispensed with. In other words, the coated surface of the photosensitive sheet can be protected against frictional force of these rollers. If the sheet is rolled up and set inside the housing structure, furthermore, it can also be safely protected against exposure to external light.
A rolled photosensitive sheet, however, risks the danger of exposure to light before it is set inside the housing structure of the image formation apparatus. Moreover, a roll of photosensitive sheet to be directly set inside the image formation apparatus is not easy to work with. Thus, there have been ideas of providing a detachably attachable cartridge inside an image formation apparatus for supporting such a roll of photosensitive sheet. A trouble with such an idea is that the cartridge must be so structured that a front edge of the rolled sheet stored inside can be easily pulled outside. When such a cartridge is set inside an image formation apparatus, the user must pull out the front edge of the sheet somehow and wrap it around the drum, etc. This, too, is a cumbersome job.
With a cartridge of a simple type intended only for an unused roll of photosensitive sheet, furthermore, there must be provided an additional space somewhere inside the housing structure of the image formation apparatus for storing the used part of the sheet. If the photosensitive sheet comprises a film of 25 .mu.m in thickness and is capable of copying 1000 images of size A4 in its longitudinal direction, the external diameter of its roll becomes about 120 mm. Not only is a cartridge larger than this size necessary but an extra space of comparable size must also be provided inside the housing structure for the used sheet.